The FAA proposes to supersede an existing airworthiness directive (AD) that applies to certain Boeing Model 747-100, 747-100B, 747-200B, 747-200C, 747-200F, 747-300, 747SR, and 747SP series airplanes. The existing AD currently requires an inspection to determine if acceptable external skin doublers are installed at the stringer 6 (S-6) lap splices, between station (STA) 340 and STA 400. For airplanes without the acceptable external skin doublers, the existing AD requires repetitive related investigative actions and corrective actions if necessary. The existing AD also provides an optional terminating modification for the repetitive related investigative actions. This proposed AD would mandate the optional terminating modification. This proposed AD results from a report of cracked fastener holes at the right S-6 lap splice between STA 340 and STA 380. We are proposing this AD to prevent cracking in the fuselage skin, which could result in rapid decompression and loss of structural integrity of the airplane.

You may examine the AD docket on the Internet at http://www.regulations.gov; or in person at the Docket Management Facility between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The AD docket contains this proposed AD, the regulatory evaluation, any comments received, and other information. The street address for the Docket Office (telephone 800-647-5527) is in the ADDRESSES section. Comments will be available in the AD docket shortly after receipt.

We invite you to send any written relevant data, views, or arguments about this proposed AD. Send your comments to an address listed under the ADDRESSES section. Include “Docket No. FAA-2008-1006; Directorate Identifier 2008-NM-110-AD” at the beginning of your comments. We specifically invite comments on the overall regulatory, economic, environmental, and energy aspects of this proposed AD. We will consider all comments received by the closing date and may amend this proposed AD because of those comments.

We will post all comments we receive, without change, to http://www.regulations.gov, including any personal information you provide. We will also post a report summarizing each substantive verbal contact we receive about this proposed AD.

On May 13, 2008, we issued AD 2008-10-15, amendment 39-15522 (73 FR 29042, May 20, 2008), for certain Boeing Model 747-100, 747-100B, 747-200B, 747-200C, 747-200F, 747-300, 747SR, and 747SP series airplanes. That AD requires an inspection to determine if acceptable external skin doublers are installed at the stringer 6 (S-6) lap splices, between station (STA) 340 and STA 400. For airplanes without the acceptable external skin doublers, that AD requires repetitive related investigative actions and corrective actions if necessary. That AD also provides an optional terminating modification for the repetitive related investigative actions. That AD resulted from a report of cracked fastener holes at the right S-6 lap splice between STA 340 and STA 380. We issued that AD to detect and correct cracking in the fuselage skin, which could result in rapid decompression and loss of the airplane.

The preamble to AD 2008-10-15 specifies that we consider the requirements “interim action” and that we were considering requiring the modification (installation of acceptable external skin doublers), which would terminate the repetitive related investigative actions. We now have determined that further rulemaking is indeed necessary, and this proposed AD follows from that determination.

We have evaluated all pertinent information and identified an unsafe condition that is likely to develop on other airplanes of the same type design. For this reason, we are proposing this AD, which would supersede AD 2008-10-15 and would retain the requirements of the existing AD. This proposed AD would also mandate the terminating action that was optional in AD 2008-10-15.

There are about 501 airplanes of the affected design in the worldwide fleet. This proposed AD would affect about 174 airplanes of U.S. registry.

The inspection for acceptable external skin doublers that is required by AD 2008-10-15 and retained in this proposed AD takes about 2 work hours per airplane, at an average labor rate of $80 per work hour. Based on these figures, the estimated cost of the inspection for U.S. operators is $27,840, or $160 per airplane.

The cost for the proposed terminating action depends upon the results of the inspections. Therefore, we cannot calculate those costs because we do not know what doubler conditions operators will find.

Title 49 of the United States Code specifies the FAA's authority to issue rules on aviation safety. Subtitle I, Section 106, describes the authority of the FAA Administrator. Subtitle VII, Aviation Programs, describes in more detail the scope of the Agency's authority.

We are issuing this rulemaking under the authority described in Subtitle VII, Part A, Subpart III, Section 44701, “General requirements.” Under that section, Congress charges the FAA with promoting safe flight of civil aircraft in air commerce by prescribing regulations for practices, methods, and procedures the Administrator finds necessary for safety in air commerce. This regulation is within the scope of that authority because it addresses an unsafe condition that is likely to exist or develop on products identified in this rulemaking action.

We have determined that this proposed AD would not have federalism implications under Executive Order 13132. This proposed AD would not have a substantial direct effect on the States, on the relationship between the national Government and the States, or on the distribution of power and responsibilities among the various levels of government.

For the reasons discussed above, I certify that the proposed regulation:

1. Is not a “significant regulatory action” under Executive Order 12866;

2. Is not a “significant rule” under the DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and

3. Will not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act.

We prepared a regulatory evaluation of the estimated costs to comply with this proposed AD and placed it in the AD docket. See the ADDRESSES section for a location to examine the regulatory evaluation.

(d) This AD results from a report of cracked fastener holes at the right stringer 6 (S-6) lap splice between station (STA) 340 and STA 380. We are issuing this AD to prevent cracking in the fuselage skin, which could result in rapid decompression and loss of structural integrity of the airplane.

(g) For airplanes identified as Group 1, Configuration 2, in Boeing Alert Service Bulletin 747-53A2748, dated May 9, 2008: At the latest of the times specified in paragraphs (g)(1), (g)(2), and (g)(3) of this AD, do an external general visual inspection to determine if acceptable external skin doublers are installed at the left- and right-side S-6 lap splices, in accordance with Part 1 of the alert service bulletin.

(1) Prior to the accumulation of 10,000 total flight cycles.

(2) Within 8,000 flight cycles after a modification was done in accordance with Boeing Service Bulletin 747-53-2253.

(3) Within 15 days or 100 flight cycles after May 20, 2008 (the effective date of AD 2008-10-15), whichever occurs first.

(h) If, during the inspection required by paragraph (g) of this AD, acceptable external skin doublers in accordance with the alert service bulletin are found installed at both the left- and right-side S-6 lap splices, no further work is required by this AD.

(i) If, during the inspection required by paragraph (g) of this AD, acceptable external skin doublers in accordance with alert service bulletin are not found installed at either the left- or right-side S-6 lap splice: Before further flight, do all applicable related investigative and corrective actions by doing all actions specified in Part 2 of the alert service bulletin. Repeat the applicable related investigative actions thereafter at intervals not to exceed 300 flight cycles until the modification specified in paragraph (j) of this AD is done.

(j) If, during the inspection required by paragraph (g) of this AD, acceptable external skin doublers as specified in the alert service bulletin are not found installed at either the left- or right-side S-6 lap splice: Within 3,000 flight cycles after doing the initial related investigative actions in paragraph (i) of this AD, or within 300 flight cycles after the effective date of this AD, whichever occurs later, install acceptable external skin doublers at both the left- and right-side S-6 lap splices, as applicable. The installation of the acceptable skin doublers is required on the side of the airplane that does not have the doublers already. The installation includes doing an open-hole high-frequency eddy current (HFEC) inspection of the skin for cracking, and trimming out cracking as applicable. Do all actions in accordance with the alert service bulletin. Doing this installation terminates the repetitive related investigative actions required by paragraph (i) of this AD.

The alert service bulletin refers to Boeing Service Bulletins 747-53-2253, Revision 3, dated March 24, 1994; and 747-53-2272, Revision 18, dated May 16, 2002; as additional sources of service information for accomplishment of the modification (installation of acceptable external skin doublers).

(2) To request a different method of compliance or a different compliance time for this AD, follow the procedures in 14 CFR 39.19. Before using any approved AMOC on any airplane to which the AMOC applies, notify your appropriate principal inspector (PI) in the FAA Flight Standards District Office (FSDO), or lacking a PI, your local FSDO.

(3) An AMOC that provides an acceptable level of safety may be used for any repair required by this AD, if it is approved by an Authorized Representative for the Boeing Commercial Airplanes Delegation Option Authorization Organization who has been authorized by the Manager, Seattle ACO, to make those findings. For a repair method to be approved, the repair must meet the certification basis of the airplane and the approval must specifically refer to this AD.

(4) AMOCs approved previously in accordance with AD 2008-10-15 are approved as AMOCs for the corresponding provisions of this AD.